Process for preparing trifluoro-



Dec- 22 1954 G. H. CRAWFORD, JR., ETAL 3,162,692

PROCESS Foa PREPARING TRIFLUORONITROSOALKANE Filed prl 25, 1963 1% L l i /22/ Uf l Arm/Qin@ United States Patent Oil ice Patented Dec. 22, 1964 3,162,692 PRCESS FOR PR'EPARiNG TRIFLUGRG- NHRSOALKANE George H. Crawford, Fir., White Bear Lahe, and David E.

Rice, Minneapolis, Minn., assignors to h'iinnesota Mining and Manufacturing Company, St. Paul, Minn., a

corporation of Delaware y Filed Apr. 23, 1963, Ser. No. 275,@50 3 Claims. (Cl. 269-647) This invention relates to a method for the preparation of peruoronitrosoalkanes. In one aspect this invention relates to the process technique for the pyrolytic conversion of triuoroacetyl nitrite to triuoronitrosomethane.

ln application Ser. No. 227,839, led October 2, 1962, there is disclosed a method for the preparation of uorinecontaining acyl nitrites, and the decarboxylation of these nitrites to produce nitroso alkanes. The decarboxylation to the nitrosoalkane may be accomplished by pyrolysis. The pyrolysis of tril'luoroacetyl nitrite is carried out in the vapor phase in view of the fact that the boiling point of the tri'luoroacetyl nitrite is below the pyrolysis temperature. This fact raises several diiculties in the production of nitrosoalkane. The gas phase pyrolysis of trifluoroacetylnitrite is uneconomical because the ratio of reactor volume to reactoroutput is very high. In addition, extreme care must be utilized in preventing the accumulation of nitrite vapor, which may cause detonation. This difficulty is not as pronounced with the higher homologs of the nitrite series since such homologs have boiling points above the pyrolysis temperature. Another method for the conversion of the nitrite to the nitrosoalkane is the photolytic decarboxylation of the nitrite with Y which technique would eliminate the above difficulties encountered with prior suggestions.

It is an object of this invention to provide a new process for the preparation of nitrosoalkanes.

lt is another object of this invention to provide a safe and economical method for the production of peruoronitrosomethane.

Still another object of this invention is to provide a method for the production of peruoronitrosomethane from trifluoroacetyl nitrite characterized by high yield and relatively low reactor volume to output ratio.

Various other objects and advantages of the present invention will become apparent to those skilled in the art from the accompanying description and disclosure.

In accordance with this invention, tritluoroacetyl nitrite is decarboxylated in the presence of a reluxing inert solvent at a pressure suicient to maintain the triiuoroacetyl nitrite in the liquid phase at the decarboxylation temperature. The inert solvent utilized is a iuorocarbon solvent, preferably a perhalouorocarbon solvent such as peruorocyclohexane (BP. 52 C.), pertluoromethyl-cyclopentane (BP. 76 C.), l,3-dichlorohexauoro-cyclobntane (BP. 59 C), peruoromethyl-cyclohexane (BP.

solvent or mixture of solvents utilized should thereforekv preferably boil at about 98 C. or lower, usually `above 70 C., at atmospheric pressure. The solvent is also preferably miscible with the trifluoroacetyl nitrite. The temperature of pyrolysis or decarboxylation of the nitrite is approximately to 170 C. Therefore the pressure utilized in the system will be sufficient to maintain the nitrite in liquid state at the decarboxylation temperature but permit refluxing or boiling of the solvent. Usually a pressure between about 50 and about lOt) pounds gauge is used which pressure may conveniently be obtained by pressuring the system with nitrogen. The nitroso alkane product boils at a temperature below the decarboxylation temperature at the pressure utilized in the system and therefore is removed as a vapor continuously from the reaction zone. The nitrite feed may be continuously introduced into the reaction Zone in order to make the process continuous. The volume ratio of solvent to nitrite in the reaction zone is at least 21l.

It is one of the important features of the present invention to remove continuously the triiuoronitrosomethane from the reaction zone as it is formed and this is accomplished by continuously removing the product through a reflux condenser in which the solvent is condensed. The system lends itself readily and conveniently to the continuous removal of tritluoronitrosomethane since it is volatile at the conditions of reaction. This continuous removal of the tritiuoronitrosomethane from-the system accounts to a large degree for the success of the process.

In the prior suggested processes as described above for gas phase pyrolytic reaction and photolysis, the concentration of trifluoronitrosomethane is intentionally maintained very low in order to prevent detonation. As a result conversions are very low and the process inefficient. By refluxing the solvent and maintaining the nitrite in the liquid phase and removing the nitroso alkane as it is formed, the process is highly etlicient and the yield is high. The nitroso alkane product from the reaction zone is passed through conventional separating and processing equipment to remove by-products and solvent and to purify the nitrosoalkane. The nitrosoalk e product is liquied for storage.

The drawing of the present application is a diagrammatic illustration, in elevation, showing a typical arrangement of apparatus in accordance with the present invention for the conversion of the nitrite to the nitrosoalkane starting with the production of the nitrite from the anhydride. In accordance with the drawing, trifluoroacetic anhydride is stored in storage vessel il under nitrogen pressure. Nitrogen sesquioxide is stored in storage vessel 12. These two reactants are passed to a metering and mixing pump 13 by means of conduits 14 and i5 and thence to a coil reactor t7 by conduit 16. The reaction is effected in reactor 17 between the triliuoroacetic anhydride and the Y Y inch gauge and the temperature is approximately 150 to C. Reflux condenser 19 is maintained at about 135 K V passing overhead through conduit Zlwith the product from reactor 21. The ow rates of trifluoroacetyl nitrite` into reactor 2l usually ranges between about 0.5 cc. per

minute to about 2.5 cc. per minute.

The pyrolysis producttritluoronitrosomethane is vaporzed in reactor 21 and is passed as a vapor from reactor 21 hrough conduit 20, reflux condenser 19 and thence hrough conduit 23 to counter-current scrubber 29. urge tank 24 and back pressure regulator 26 are proyided on conduit 23 to maintain the pressure in the sysem substantially constant. The back pressure regulator L6 is set so that gas generated by the reactor will be bled )E as the pressure builds up in excess of the pre-set value. l`he back pressure regulator 26 must be accurate and mainain the pressure at a constant level of about i2 lbs. per ;quare inch gauge. Otherwise pressure surges and drops vill cause periodic ooding of reflux condensor 19 and xcess entrainment of solvent and nitrite into the surge `ank 24. The gas bled from the back pressure regulator Z6 has passed through a series of traps (not shown) comv)rising a first Dry Ice trap followed by a liquid nitrogen rap to recover reactants and product.

In counter-current scrubber 29, triuoronitrosomethane s scrubbed with water introduced into the top of scrubber 9 through conduit 31 and removed at the bottom through :onduit 38. Scrubber 29 removed carbon dioxide and my entrained nitrite. From scrubber 29 the scrubbed triuoronitrosomethane is passed through a molecular sieve 53 by means of conduit 32. The molecular sieve removes :he last trace of impurities in the triuoronitrosomethane product. From molecular sieve 33 the puried trifluoro nitrosomethane passes through conduit 34- to accumulator Jr storage unit 36 which is maintained slightly above liqlid nitrogen temperature. The tritluoronitrosomethane is condensed in cooler-storage vessel 36 and maintained therein as a liquid. Nitrogen is removed by means of conduit 39. In addition to or in place of the molecular sieve 33 a fractional distillation unit may be employed to further purify the trifluoronitrosomethane.

The relative boiling points of solvent or diluent and nitrite are preferably selected such that under the condition of pyrolysis the distribution of nitrite between the vapor phase and liquid phase favors a higher concentration of ni-trile in liquid phase. Various processes and conditions and alterations and modications of the process may be practiced and become obvious to those `skilled in the art Without departing from the invention.

Having described our invention, We claim:

l. A process for decarboxylating a uorinated acyl nitrite which comprises introducing iiuorinated acyl nitrite into a reaction zone which is at the pyrolysis temperature of the nitrite containing a uorocarbon solvent having a boiling point below the boiling point of the uorinated acyl nitrite, maintaining a pressure in the reaction zone suicient to maintain the iluorinated acyl nitrite in the liquid phase but such as to permit reiiuxing or boiling of the uorocarbon solvent and continuously removing vaporous uorinated nitrosoalkane as a product of the process from the reaction zone.

2. A process for decarboxylating trifiuoroacetyl nitrite which comprises introducing triiiuoroacetyl nitrite into a reaction zone which is at the pyrolysis temperature of the nitrite containing a perhalouorocarbon solvent having a boiling point below the boiling point of the triuoroacetyl nitrite, maintaining a pressure in the reaction zone sufcient to maintain the trifluoroacetyl nitrite in the liquid phase but such as `to permit reuxing or boiling of the fluorocarbon solvent and continuously removing vaporous triuoronitrosomethane as a product of the process from the reaction zone.

3. A process for decarboxylating tritluoroacetyl nitrite which comprises introducing triuoroacetyl nitrite into a reaction zone which is at a temperature of about 150 to 170 C. containing a perhaloiiuorocarbon solvent comprising a mixture of periiuorocyclic ethers boiling at about 97 to 98 C. at atmospheric pressure in an amount by volume of at least twice the nitrite in the reaction zone, maintaining a pressure in the reaction zone sufficient to maintain the triuoroacetyl nitrite in the liquid phase but such as to permit refluxing or boiling of the fluorocarbon solvent and continuously removing vaporous triuoronitrosomethane as a product of the process from the reaction zone.

No references cited, 

1. A PROCESS FOR DECARBOXYLATING A FLUORINATED ACYL NITRITE WHICH COMPRISES INTRODUCING FLUORINATED ACYL NITRITE INTO A REACTION ZONE WHICH IS THE PYROLYSIS TEMPERATURE OF THE NITRITE CONTAINING A FLUOROCARBON SOLVENT HAVING A BOILING POINT BELOW THE BOILING POINT OF THE FLUORINATED ACYL NITRITE, MAINTAINING A PRESSURE OF THE REACTION ZONE SUFFICIENT TO MAINTAIN THE FLUORINATED ACYL NITRITE IN THE LIQUID PHASE BUT SUCH AS TO PERMIT REFLUXING OR BOILING OF THE FLUOROCARBON SOLVENT AND CONTINUOUSLY REMOVING VAPOROUS FLUORINATED NITROSOALKANE AS A PRODUCT OF THE PROCESS FROM THE REACTION ZONE. 